| Summary: | We report clear room temperature ambipolar transport in ambient-air processed methylammonium lead iodide (MAPbI<sub>3</sub>) thin-film transistors (TFTs) with aluminum oxide gate-insulators and indium-zinc-oxide source/drain electrodes. The high ionicity of the MAPbI<sub>3</sub> leads to p-type and n-type self-doping, and depending on the applied bias we show that simultaneous or selective transport of electrons and/or holes is possible in a single MAPbI<sub>3</sub> TFT. The electron transport (n-type), however, is slightly more pronounced than the hole transport (p-type), and the respective channel resistances range from 5−11 and 44−55 MΩ/μm. Both p-type and n-type TFTs show good on-state characteristics for low driving voltages. It is also shown here that the on-state current of the n-type and p-type TFTs is highest in the slightly PbI<sub>2</sub>-rich and MAI-rich films, respectively, suggesting controllable n-type or p-type transport by varying precursor ratio.
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